Sensors belong to modern devices for measuring physical, chemical and biological quantities.
Modern sensors such as electrical, optical and mechanical sensors rely on various methods. One of the approaches used in optical sensors is the spectroscopy of surface plasmons. Surface plasmons are electromagnetic waves, which can be excited at an interface between a metal and a dielectric medium (Raethec Surface plasmons on smooth and rough surfaces and on gratings, Springer-Verlag, Berlin, 1988). As the electromagnetic field of surface plasmons is highly localized at the surface of the metal, surface plasmons are extremely sensitive to changes in optical parameters occurring in the vicinity of the surface of the metal. In optical sensors, surface plasmons are usually optically excited with an electromagnetic wave in the visible or near infrared spectrum. The resonant condition for excitation of the surface plasmons with an electromagnetic wave depends on a refractive index of the dielectric medium in the proximity of the metal surface. Therefore, variations in the refractive index can be monitored from the changes in the interaction between an electromagnetic wave and a surface plasmon. Surface plasmon resonance (SPR) sensors can be used as highly sensitive refractometers and can also be applied to the study of biomolecules and their interactions and for detection of chemical and biological compounds. In these applications, SPR sensors are combined with biorecognition elements, which specifically interact with an analyte (e.g., antibody, enzymes, and DNA). The interaction between the immobilized biorecognition element on the sensor surface and the analyte in a liquid sample increases a refractive index in the proximity of the surface of the sensor. This refractive index change can be detected by means of optically excited surface plasmons.
There are numerous configurations of surface plasmon resonance (SPR) sensors. These include configurations employing prism couplers (Sensors and Actuators, 4 (1983) 299-304; Electronics Letters, 23 (1988) 1469-1470), grating couplers (Sensors and Actuators B, 8 (1992) 155-160), optical fibers (Sensors and Actuators B, 12 (1993) 213-220; Analytical Chemistry, 66 (1994) 963-970) and integrated optical waveguides (Sensors and Actuators B, 12 (1993) 213-220; Analytical Chemistry, 66 (1994) 963-970). In grating-based SPR sensors, an interaction between an electromagnetic wave and a surface plasmon is detected by measuring changes in intensity (Biosensors, 3 (1987/88) 211-225), angular spectrum (American Laboratory, 33 (2001) 37-40) or wavelength spectrum (Measurements and Science Technology, 6 (1995) 1193-1200) of an electromagnetic wave reflected from a grating coupler. For parallel detection of multiple chemical or biological compounds, or for parallel monitoring of their interactions, multichannel SPR sensors are used. In multichannel SPR sensors, using grating couplers, the resonant interaction between an electromagnetic wave and surfaces surface plasmons can be detected in a spatial distribution of an angular reflected spectrum (American Laboratory, 33 (2001) 37-40). Recently, a method for multichannel SPR sensor based on a prism coupler and sequential excitation of surface plasmons was described in Czech patent No. 291 728 (J. {hacek over (C)}tyroký, J. Dostálek, J. Homola).